The present invention relates, in general, to integrated circuits and, more particularly, to a capacitor structure for an integrated circuit that has a conductive trench.
Capacitors are a fundamental component of a typical integrated circuit, and numerous capacitor structures exist depending on the particular circuit application desired. One such structure is known as a "bypass capacitor", which is used for example to reduce noise on voltage supply lines for integrated circuits operating at high frequencies.
A typical prior bypass capacitor uses a top electrode of metal, a bottom electrode of heavy-doped polysilicon, and a dielectric of silicon nitride. However, a disadvantage of this prior capacitor is that the bottom electrode requires a metal contact formed through some of the overlying layers of the integrated circuit. This contact to the bottom electrode requires additional surface area on the integrated circuit and causes a significantly high series resistance across the bottom electrode. This is so because the bottom electrode typically has a sheet resistance of about 140 ohms/square, and the contact to the bottom electrode is usually made at only one end of the electrode. Thus, there exists a high resistance across the bottom electrode from the contacted end to the opposite end of the electrode. A further disadvantage of this prior capacitor is that either the metal contact to the top electrode or the metal contact to the bottom electrode must be routed across the top of the integrated circuit layout for connection to a ground or other lowest potential source.
Accordingly, there is a need for an integrated circuit capacitor that reduces the series resistance of the bottom electrode, reduces the integrated circuit surface area required for the capacitor, and eliminates the need for metal routing over the surface of the integrated circuit to connect a capacitor electrode to a lowest potential source.